++ Very useful node, thanks gmax.
For the sake of portability it might also be useful to note that ANSI SQL-92 provides a standard for querying table schema information:
select TABLE_NAME from INFORMATION_SCHEMA.TABLES
And to give an idea of what else is available via INFORMATION_SCHEMA;
SCHEMATA
DOMAINS
VIEWS
COLUMNS
TABLE_PRIVILEGES
COLUMN_PRIVILEGES
USAGE_PRIVILEGES
DOMAIN_CONSTRAINTS
TABLE_CONSTRAINTS
REFERENTIAL_CONSTRAINTS
CHECK_CONSTRAINTS
KEY_COLUMN_USAGE
ASSERTIONS
VIEW_TABLE_USAGE
VIEW_COLUMN_USAGE
CONSTRAINT_TABLE_USAGE
CONSTRAINT_COLUMN_USAGE
CONSTRAINT_DOMAIN_USAGE
Source: An Introduction to Database Systems (7th edition), C.J. Date 